1. Field of the Invention
The present invention relates to a modified polynucleotide, in which an initiation codon is substituted with ATG, a vector comprising the same, a microorganism comprising the polynucleotide, and a method for producing L-lysine using the same.
2. Description of the Related Art
Strains of the genus Corynebacterium, specifically Corynebacterium glutamicum, are Gram-positive microorganisms which are extensively used to produce L-lysine. L-lysine is used, for animals feed, medicines and cosmetics for humans, and is produced through fermentation of the Corynebacterium strain.
Conventionally, a strain of the genus Corynebacterium having enhanced lysine biosynthesis genes and a method of producing L-lysine using the same are known. For example, U.S. Pat. No. 6,746,855 discloses a method for producing L-lysine by culturing Corynebacterium which has an enhanced expression of lysE gene (lysine export carrier gene), and additionally introduced genes selected from the group consisting of a dapA gene, a lysC gene, a pyc gene and a dapB gene.
Another method is to amplify genes on the lysine biosynthesis pathway or to modify a promoter. For example, Korean Patent application laid-open Nos. 2009-0082702 and 2009-0084099 disclose a method for producing L-lysine by introducing improved promoters of ddh and lysC-asd operon into Corynebacterium. Korean Patent application laid-open No. 2008-0025355 discloses a method for improving lysine productivity by amplifying the copy number of the genes on the lysine biosynthesis pathway, which are aspB, lysC, asd, dapA, daps, lysA, and pyc, in the chromosome.
Meanwhile, the initiation codon which is recognized by ribosomes to initiate translation in the chromosome is usually ATG. Translation can be controlled according to the initiation codon of the gene, and the sequence of the initiation codon is important in the regulation of protein activity. However, while ATG is the common initiation codon among the lysine biosynthesis genes derived from Corynebacterium glutamicum, the initiation codon of lysC and pyc genes is GTG, and TTG is for tkt gene on pentose phosphate pathway contains the initiation codon of TTG (reference: J. Biotechnol., 104: 5-25, 2003.)
The present inventors have made many efforts to find a method for improving lysine productivity, and as a result, they found that the initiation codon of the wild-type lysC, tkt and pyc genes can be substituted with ATG to enhance the activities of aspartate kinase, transketolase and pyruvate carboxylase over their endogenous activities, thereby completing the present invention.